1. Field of the Invention
This invention relates to fluid-powered hand-held devices for body care, particularly for tooth care and mouth care.
2. Description of the Prior Art
In known hand-held devices of this kind, such as those disclosed in U.S. Pat. Nos. 3,536,065 and 3,771,186, the hydraulic piston motor is arranged concentric with or in the longitudinal axis of the device casing. During the operation of the hydraulic motor the piston thereof is reciprocatorily driven in the axial direction of the device casing by the pressure pulses produced by the liquid pump and sets the instrument holder into an oscillating rotary motion about its longitudinal axis by means of a motion converter. The hydraulic motor is inoperative when a pushed-on spraying nozzle is used which is fed through the liquid duct in the device casing.
One prior art motion converter consists of a driving sleeve which is freely rotatably, but axially non-displaceably mounted in continuation of the motor cylinder and has a helical groove provided in its peripheral wall; the leading end of the piston enters into the driving sleeve and supports a radial pin which engages into the helical groove and thus converts the axial reciprocatory motion of the piston into an oscillating rotation of the driving sleeve. Typically a pin and slot connection or a spring aim and detent connection are used for removably attaching the treatment instruments.
These known devices require a plurality of co-operating movable parts which cause abrasion effects and reduce the efficiency of the drive because of the motion converter and because of their mechanical friction. Furthermore in devices that include a motion converter the course of the feed pipe for the spraying nozzle in the device casing is rather complicated.